1. Field of the Invention
The present invention relates to a process for producing an optical recording medium suited for carrying out optical recording and/or reproduction using a laser beam or the like.
2. Related Background Art
Optical information recording mediums such as optical disks and optical cards comprises a substrate and provided thereon a thin recording layer on which optically detectable minute pits of about several .mu.m are formed in the form of tracks. Information can be thus recorded in a high density.
A process for producing such information recording mediums comprises a step of forming a grooved preformat on the support, a step of forming a recording layer, a step of forming a protective layer, and so forth. Of these, known as methods used in the formation of the support include an injection method, a compression method, and a photopolymerization method using an ultraviolet-curable resin (herein after "2OP method").
In these production processes, the information recording medium as a whole is usually prepared in an individual sheet (hereinafter called sheet-by-sheet process). The reason for the sheet-by-sheet process having been mostly adopted is because spin coating is mostly used in solution coating when the recording layer is provided, and, in view of the alignment required when the protective layer and an adhesive layer are provided.
The sheet-by-sheet process, however, results in an increase in the time required for the processing steps, and is not suited for production processes aiming at low cost and an improvement in operability.
In the instance of the 2P method, the ultraviolet-curable resin commonly used includes polyester acrylate, epoxy acrylate and urethane acrylate, which belong to a radical polymerization type. These, however, may be inhibited from curing because of the presence of oxygen in the air. Hence, there has been the problem that the resin is not well cured at the central hole and peripheral part of the disk, so that unreacted monomers remain in the resin, and these residual monomers diffuse in the recording layer, resulting in a deterioration of the recording layer.
As a countermeasure to cope with this problem, one may contemplate a method in which the curing is carried out in an inert gas or a method in which the unreacted portion is removed using a solvent or cut away, but both of them bring about complicated steps when conventional production processes are used.
In forming the protective layer, it is also common to use a material having the same size as, and similar shape to, the substrate, where it has been required for each sheet to be processed in the desired shape, size and thickness and then aligned. Further, a similar problem has remained in each functional layer and adhesive layer. Moreover, the dust produced at end surfaces of the substrate may be often included into the recording layer and protective layer when the recording layer is formed or the protective layer is laminated, resulting in a lowering of the yield of products.